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openat — open a file relative to a directory file descriptor
#include <fcntl.h>
int
openat( |
int dirfd, |
const char *pathname, | |
int flags) ; |
int
openat( |
int dirfd, |
const char *pathname, | |
int flags, | |
mode_t mode) ; |
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Note | |||||
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The openat
() system call
operates in exactly the same way as open(2), except for the
differences described in this manual page.
If the pathname given in pathname
is relative, then it
is interpreted relative to the directory referred to by the
file descriptor dirfd
(rather than relative to the current working directory of the
calling process, as is done by open(2) for a relative
pathname).
If pathname
is
relative and dirfd
is
the special value AT_FDCWD
,
then pathname
is
interpreted relative to the current working directory of the
calling process (like open(2)).
If pathname
is
absolute, then dirfd
is ignored.
On success, openat
() returns
a new file descriptor. On error, −1 is returned and
errno
is set to indicate the
error.
The same errors that occur for open(2) can also occur for
openat
(). The following
additional errors can occur for openat
():
dirfd
is not
a valid file descriptor.
pathname
is
relative and dirfd
is a file
descriptor referring to a file other than a
directory.
openat
() was added to Linux
in kernel 2.6.16; library support was added to glibc in
version 2.4.
openat
() and other similar
system calls suffixed "at" are supported for two reasons.
First, openat
() allows an
application to avoid race conditions that could occur when
using open(2) to open files in
directories other than the current working directory. These
race conditions result from the fact that some component of
the directory prefix given to open(2) could be changed in
parallel with the call to open(2). Such races can be
avoided by opening a file descriptor for the target
directory, and then specifying that file descriptor as the
dirfd
argument of
openat
().
Second, openat
() allows the
implementation of a per-thread "current working directory",
via file descriptor(s) maintained by the application. (This
functionality can also be obtained by tricks based on the use
of /proc/self/fd/
, but less
efficiently.)dirfd
faccessat(2), fchmodat(2), fchownat(2), fstatat(2), futimesat(2), linkat(2), mkdirat(2), mknodat(2), open(2), readlinkat(2), renameat(2), symlinkat(2), unlinkat(2), utimensat(2), mkfifoat(3), path_resolution(7)